In general, a differential gear apparatus for vehicles includes a plurality of planetary gears which can rotate and revolve. Each planetary gear is rotatably (about its own axis) received in a receiving hole formed in a carrier (see Official Gazettes of Japanese Patent Application Laid-Open Nos. H04-312247, H09-112657 and 2002-89659).
Since the planetary gear rotates about its own axis, its outer peripheral surface slide-contacts the inner peripheral surface of the receiving hole. Moreover, the end face of the planetary gear slide-contacts the bottom surface of the receiving hole or a member for axially supporting the planetary gear. Owing to this arrangement, in the conventional differential gear apparatus, there is such a problem that the planetary gear is easily worn out early.
One example of such a problem will now be described in more detail. FIG. 4 is a sectional view showing a state in which a planetary gear P is received in a receiving hole Q1 of a carrier Q. The inside diameter of the receiving hole Q1 is set to be larger than the outside diameter of the planetary gear P so that the planetary gear P can rotate about its own axis and a lubricant can be received between the inner peripheral surface of the receiving hole Q1 and the outer peripheral surface of the planetary gear P. When the outer peripheral surface of the planetary gear P is pressed against the inner peripheral surface of the receiving hole Q1, in a case wherein the inside diameter of the receiving hole Q1 is set to be larger than the outside diameter of the planetary gear Q, the contact area between the inner peripheral surface of the receiving hole Q1 and the outer peripheral surface of the planetary gear P is reduced compared with a case wherein the inside diameter of the receiving hole Q1 is set to be equal to the outside diameter of the planetary gear P. For this reason, the outer peripheral surface of the planetary gear P is easily worn out early.